Process for brightening zinc and cadmium electroplate using an inner salt of a quaternized pyridine carboxylic acid and compositions containing the same



United States Patent O f 3,411,996 PROCESS FOR BRIGHTENING ZINC AND CAD- MIUM ELECTROPLATE USING AN INNER SALT OF A QUATERNIZED PYRIDINE CAR- BOXYLIC ACID AND COMPOSITIONS CON- TAINING THE SAME John D. Rushmere, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 511,245, Dec. 2, 1965. This application Sept. 20, 1967, Ser. No. 669,309

16 Claims. (Cl. 204-50) ABSTRACT OF THE DISCLOSURE It has been found that the addition of an inner salt of a quaternized pyridine carboxylic acid to aqueous alkaline electroplating baths containing zinc and cadmium ions provides smooth, bright deposit of these metals. High plating efliciency with low consumption of the inner salt of the quaternized pyridine compound is obtained using it alone or in combination with other bath additives.

CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 511,245 filed D c. 2, 1965, now abandoned.

SUMMARY OF INVENTION According to the present invention there is provided an aqueous, alkaline electroplating bath containing metal ions selected from the group consisting of zinc and cadmium having the improvement comprising an inner salt of a quaternized pyridine carboxylic acid having the formula COO wherein R is hydrogen or dissolv d therein in an amount to yield a metal deposit of improved brightness.

The invention also comprises the process for electroplating zinc and cadmium from an aqueous, alkaline electroplating bath which comprises adding to the bath from about 0.1 to about grams/liter of an inner salt of a quaternized pyridine carboxylic acid of the above formula.

The invention is also an aqueous addition agent for an electroplating bath containing zinc or cadmium ions comprising from about 1:100 to 100:1 parts by weight of an inner salt of a quaternized pyridine carboxylic acid of the above formula and a bath soluble organic polymer.

DETAILED DESCRIPTION OF INVENTION The inner salt of a quaternized pyridine carboxylic acid must be soluble in the bath, i.e., having a solubility of at least about 0.01 gram/ liter at a temperature of about 25 C. The compounds may be obtained from commercial 3,411,996 Patented Nov. 19, 1968 wherein R is hydrogen or COO- Preferred compounds are l-benzyl pyridinium 3-carboxylate and p-xylylene bis(pyridinium 3-carboxylate).

The quarternized pyridine inner salts are preferably used in combination with organic polymers which are also soluble in the bath. The presence of the polymer is particularly desirable when the bath is used at temperatures above room temperature. The quaternized pyridine inner salt may generally be used alone at a temperature from about 20 C. to 30 C.; however, at the higher temperatures, i.e., 30 C. to 50 C., it is usually desirable to use both a quaternized pyridine inner salt and an organic polymer.

Examples of suitable polymers include synthetic polymers such as polyvinyl alcohol and polyethylene amine, and natural polymers such as gelatin, glue, p ptone, gum tragacanth, gum arabic, gum ghatti, gum guaiac, and agaragar as well as protein substances such as egg albumin and milk protein hydrolysate. The polyvinyl alcohol may be modified, e.g., a partial ether formed by condensation with ethylene oxide or glycidol. The polyvinyl alcohols prepared by hydrolysis of polyvinyl acetate are a preferred type of organic polymer. Those having average molecular weights from about 5,000 to 20,000 which are either fully hydrolyzed or partially hydrolyzed (87%- 89%) provide particularly stable plating baths.

The brightening compositions of this invention are preferably used in the form of aqueous addition agents for the zinc and cadmium plating baths. Additives for the plating baths may be prepared containing from about 1:100 to :1 parts by weight of the quaternized pyridine inner salt and organic polymer. The addition agent preferably consists of an aqueous solution containing from about 5 to 35% by weight of solids and is added directly to the bath. Preferably, the additive will contain from about 3:1 to 9:1 parts by Weight of quaternized pyridine inner salt to polymer.

In preparing the plating baths, zinc and cadmium ions are made available in the usual manner by adding oxides, hydroxides and cyanides of these metals to the plating bath. The bath should be alkaline in nature since the quaternized pyridine inner salts tend to be ineffective as brightening agents under acid conditions. In a preferred electroplating bath containing zinc or cadmium, from about 0.1 to 10 grams/liter of a quaternized pyridine inner salt will be present with from about 0.01 to 10 grams/ liter of the organic polymer.

The invention will be further illustrated by the following examples in which parts and percentages are by weight unless otherwise specified. In the examples both barrel and still plating operations were carried out.

Example H Example I was repeated except that 115 grams/liter of sodium cyanide were used in the bath and 30 grams/liter of cadmium oxide were substituted for the zinc cyanide.

Example I 5 Test 5: Demonstrating brightness range-A steel Hull cell panel was plated at 1 amp. for 5 minutes in a cad- In a seiies of experiments, an aqueous plating bath qg glg g g zgi g giig' i I -enzy pyri 1m -car a. rw havmg the following composmon was prepared short dip in 0.5 weight percent nitric acid, a smooth bright G /li plate was obtained over the range 10-60 amp./ sq. ft.

Sodium cyanidfi 40 A control panel plated under similar conditi ns bu in Sodium hydroxide 90 the absence of the quaternized pyridinium inner Salt had Zinc cyanide 0 a dull White plate across the entire face of the panel.

Sodium carbonate 30 Test 6 Demonstrating utility in practical still plating.

Sodium lfid 1 1 A steel Hull cell panel bent in the form of a rectangular Z shape was plated at 2 amp. for minutes in a cyal-benzyl pyridinium 3-carboxylate was prepared by quanide bath containing 0.5 gram/liter of l-benzyl pyridinium ternizing 1 mole of nicotinic acid (123 grams) with 1 3-carboxylate. After bright dipping in :a dilute H O mole of benzyl chloride (126 grains) in 400 grams of H 80 bright dip, the Work showed a nice bright shiny water. Suflicient sodium hydroxide was added to the reacplate extending all the way into the recesses of the 2 tion mixture to give a pH of 6.0 to 6.5. The mixture was which demonstrates the excellent throwing power of the then refluxed for three hours, cooled, and diluted to give plating bath.

a 10% by weight solution which was added to the cyanide By comparison, a control piece plated in the absence of plating bath. the quaternized pyridinium inner salt showed a semi- Test 1: Demonstrating wide brightness range.A steel bright matte plate.

Hull cell panel was plated at 2 amp. for 5 minutes in a Example VI bath containing 0.8 gram/liter of l-benzyl pyridinium 3- carboxylate. After washing and a dip in 0.5 weight perffai f,fi ggfi ggllbfivaz ri teii bath cent nitric acid to r move stains, an extremely bright plate 6 g p p p was obtained over the current density range 4-150 amp./ Grams/lit sq. ft. In a control experiment conducted in the absence of Sodium cyanide 40 any additive, a uniformly dull plate over the entire face Sodium -Q; u 90 of the panel was obtained (1150 amp./ sq. ft.). Zinc cyanide 60 Test 2: Demonstrating utility in practical still plating.-- Sodium carbonate 30 A steel crank hole cover was plated at 2 amp. for 15 min- Utes 111 a f P g bath containing Q8 gtam/htel' A series of inner salts quaternized pyrinium compounds y Plf Q Y t After Washlhg h a were prepared by refluxing 0.1 mole of a pyridine carl} 1H Welght P Cent llltllc acld, an extremely bright boxylic acid and an equimolar quantity of a quaternizing 3 Plate w Obtahled 011 all Surfaces, 6W1! those of 10W agent in 100 cc. of water. The reaction was judged as havculreht y- 40 ing taken place by the disappearance of the oily appear- T 2 Was repeated eXCBPt that a Serles of ance of the quaternizing agent or change in color of the crank hole covers were plated successively in the bath to flu The mixture was cooled and then diluted to give h Was added? Partially y yh P a 10 weight percent solution of the resulting inner salt of f y' alcohol h'avlllg a molecular Welght of about 16,800 a quaternized pyridinium compound. :In the series of tests with the amount of P W Y alcohol being increased after reported in Table 2 which follows, the quaternized pyrieach plating operation. The following observations were di i compound was dd d t h l ti b th i a made 011 the Plated Products, demtmstlatiflg that even amount of about 0.8 gram/liter. All of the quaternized very small amounts of polyvinyl alcohol impr v the pyridinium compounds were found to be effective brightenquality of the electroplate over that obtained by either i agents compound alone.

TABLE 2 TABLE 1 TbIest Pyridine Compound Quaterni'zing Agent l-benzyl Polyvinyl 0' pyridinium alcohol Prod ct quality Pyridine 4-carboxylic acid Benzyl chloride. 3-carboxylate added, g./1. 8 Pyridine 3,5-dicarboxylic acid Do.

added, g.ll. 9. Pyridine B-carboxylic acid (2 mols) a,a'-Di0hl0!'0 p-xylene.

(a)- 0.8 0 vilgafiegggglgfoduct. Bright What is d aim e d is:

( 0-004 Brightness u c a as 1. In an aqueous alkaline electroplating bath contain- (a). Increase in shininess 0i mam ing metal ions selected from the group consisting of zinc ii?) n 8'; 8'8 gimduct about the same and cadmium, the improvement which comprises an inner ate very bright and shiny.

hnprgved over salt of a quaternized pyridine carboxylic acid having the (e) 0. S 0 Plate has extremely bright and f l liquid appearance even in low current density areas.

Over-all mirror-like quality. (f) 0 0. 13 Dull on all surfaces. 6 5

COO

Test 4: Demonstrating utility in practical barrel plat- I ing.One hundred grams steel screws were barrel plated CH 1 at 3 amp. for 30 minutes in a zinc cyanide plating bath I containing 0.8 gram/liter of l-benzyl pyridinium 3-carboxylate. The screws produced were very shiny and showed little staining. They were not significantly improved in quality by a dip in 0.5 weight percent nitric acid. R

wherein R is hydrogen or dissolved therein in an amount to yield a metal deposit of improved brightness.

2. The electroplating bath of claim 1 wherein the inner salt of a quaternized pyridine carboxylic acid is l-benzyl pyridinium 3-carboxylate.

3. The electroplating bath of claim 1 wherein the inner salt of 1a quaternized pyridine carboxylic acid is p-Xylylene bis(pyridinium 3-carboxylate).

4. The electroplating bath of claim 1 wherein the bath is a cyanide bath.

5. In the process for electrodepositing a metal from an aqueous alkaline electroplating bath containing metal ions selected from the group consisting of zinc and cadmium, the improvement which comprises having present in said bath from about 0.1 to about grams/liter of an inner salt of a quaternized pyridine carboxylic acid having the formula wherein R is hydrogen or 6. The process of claim 5 wherein the inner salt of a quaternized pyridine carboxylic acid is l-benzyl pyridinium 3-carboxylate.

7. The process of claim 5 wherein the inner salt of a quaternized pyridinium carboxylic acid is p-xylylene bis (pyridinium 3-carboxylate) 8. The process of claim 5 wherein a bath soluble organic polymer is present in the bath in an amount from about 0.01 to about 10 grams/liter.

9. The process of claim 8 wherein the bath soluble organic polymer is a polyvinyl alcohol having a molecular weight between about 5,000 and 20,000.

10. The process of claim 5 wherein the electroplating bath is a cyanide bath.

11. An aqueous addition agent for an electroplating bath containing metal ions selected from the group consisting of zinc and cadmium consisting essentially of from about 1:100 to 10021 parts by weight of an inner salt of a quaternized pyridine carboxylic acid having the formula I j oom \N+ wherein R is hydrogen or and a bath soluble organic polymer.

12. The composition of claim 11 wherein said addition agent contains from about 5 to 35% by weight of solids.

13. The composition of claim 11 wherein the inner salt of a quaternized pyridine carboxylic acid is l-benzyl pyridinium 3-carboxylate and the bath soluble organic polymer is a polyvinyl alcohol having a molecular weight between about 5,000 and 20,000.

14. The composition of claim 13 wherein the composition contains from about 3:1 to about 9:1 parts by weight of said l-benzyl pyridinium 3-carboxylate to said polyvinyl alcohol.

15. The composition of claim 11 wherein the inner salt of a quaternized pyridine carboxylic acid is p-Xylylene bis(pyridinium 3-earboxylate) and the organic polymer is a polyvinyl alcohol having a molecular weight between about 5,000 and 20,000.

16. The composition of claim 15 wherein the composition contains from about 3:1 to about 9: 1 parts by weight of said p-xylylene bis(pyridinium 3-carboxylate) to said polyvinyl alcohol.

References Cited UNITED STATES PATENTS 1,536,859 5/1925 Humphries 204 2,080,520 5/1937 Westbrook 204 2,171,842 9/1939 Barrett et al 20450 XR 2,803,593 8/1957 High et a1. 20450 3,317,412 5/ 1967 Dahlmann 20455 3,318,787 5/1967 Rindt et al 20455 HOWARD S. WILLIAMS, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

